United States Patent [19J
`Takeuchi et al.
`
`[54] FLAT LIGHT SOURCE USING LIGHT(cid:173)
`DIFFUSING SHEET WITH PROJECTIONS
`THEREON
`
`[75]
`
`Inventors: Michiko Takeuchi; Toshikazu Nishio;
`Taiji Ishii, all of Tokyo-To, Japan
`
`[73]
`
`Assignee: Dai Nippon Printing Co., Ltd., Japan
`
`[ * l
`
`Notice:
`
`This patent issued on a continued pros(cid:173)
`ecution application filed under 37 CFR
`1.53( d), and is subject to the twenty year
`patent term provisions of 35 U.S.C.
`154(a)(2).
`
`[21] Appl. No.:
`
`08/619,623
`
`[22] PCT Filed:
`
`Aug. 11, 1995
`
`[86] PCT No.:
`
`PCT/JP95/01608
`
`§ 371 Date:
`
`May 30, 1996
`
`§ 102(e) Date: May 30, 1996
`
`[87] PCT Pub. No.: W096/05466
`
`PCT Pub. Date: Feb. 22, 1996
`
`[30]
`
`Foreign Application Priority Data
`
`Aug. 12, 1994
`
`[JP]
`
`Japan .................................... 6-210694
`
`Int. Cl.6
`........................................................ F21 V 7/04
`[51]
`[52] U.S. Cl. ............................................... 362/31; 362/551
`[58] Field of Search ................................. 362/26, 31, 551
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,729,067
`4,729,068
`4,775,222
`4,998,804
`5,262,928
`5,289,351
`5,408,388
`5,442,523
`5,467,208
`5,467,417
`
`3/1988 Ohe ........................................... 362/26
`3/1988 Ohe ........................................... 362/26
`10/1988 Ohe ........................................... 362/26
`3/1991 Horiuchi ................................... 362/26
`11/1993 Kashima eta!. .......................... 362/26
`2/1994 Kashima eta!. .......................... 362/26
`4/1995 Kobayashi et a!. ....................... 362/26
`8/1995 Kashima et a!. .......................... 362/26
`.......................... 362/26
`11/1995 Kokawa et a!.
`11/1995 Nakamura et a!.
`....................... 362/26
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US005944405A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,944,405
`*Aug. 31, 1999
`
`5/1996 Beeson eta!. ............................ 362/26
`5,521,725
`5/1996 Kashima eta!. .......................... 362/26
`5,521,797
`5,572,411 11/1996 Watai eta!. .............................. 362/31
`5,598,280
`1!1997 Nishio et a!. ............................. 362/31
`5,641,219
`6/1997 Mizobe ..................................... 362/26
`
`FOREIGN PATENT DOCUMENTS
`
`9/1980
`3/1986
`1!1987
`4/1989
`9/1989
`1!1991
`9/1992
`8/1993
`2/1994
`
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`
`55-162201
`61-55684
`62-3226
`1-112202
`1-245220
`3-9306
`4-107201
`5-196940
`6-15008
`Primary Examiner-Sandra O'Shea
`Assistant Examiner-Marshall Honeyman
`Attorney, Agent, or Firm---Parkhurst & Wendel LLP
`ABSTRACT
`
`[57]
`
`A fiat light source used as back-lighting for a liquid crystal
`display device includes an optically conductive plate (1)
`having a light reflecting layer (2), and a light source (3). A
`light-diffusing sheet (8) is provided outside the optically
`conductive plate (1) opposite to the light reflecting layer (2).
`A lens sheet ( 4) is provided outside the light-diffusing sheet
`(8), with a transmission type of display element (6) provided
`on the outer side of the lens sheet ( 4). The light-diffusing
`sheet (8) is formed of a transparent material free from
`light-diffusing agent particles and has minute irregularities
`(41) formed at random on the front surface thereof. The
`irregularities are of a surface roughness that is at least the
`wavelength of the light from the light source, but is no more
`than 100 ,urn. When the percentage of the cumulative fre(cid:173)
`quency distribution of the heights of the minute irregularities
`are plotted along the Y-axis and the heights of these minute
`irregularities are plotted along the X-axis, the cumulative
`frequency distribution curve has a convex portion oriented
`towards the lower side of the coordinates and the average
`value of the heights of the minute irregularities is greater
`than the median value thereof. Thus, a fiat light source is
`provided which emits highly luminant light uniformly
`within a predetermined angular range, and which has no
`local differences in intensity over the surface thereof.
`
`11 Claims, 20 Drawing Sheets
`
`Mercedes-Benz Ex. 1021
`
`MBI_001887
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 1 of 20
`
`5,944,405
`
`6
`
`100
`
`6
`
`100
`
`2
`
`10
`F I G. I
`
`\
`
`I I
`
`, ~ ~ --
`I; , ..,.,,
`I
`3
`/' ',:
`' I 3
`I
`I (
`\
`,_1
`I
`\ I ,J
`\L- ..::-:.__--- ----:_---_I
`
`I
`
`F I G. 2
`
`MBI_001888
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 2 of 20
`
`5,944,405
`
`F I G. 3
`
`41
`FIG. 4
`
`MBI_001889
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 3 of 20
`
`5,944,405
`
`F I G. 5
`
`F I G. 6
`
`F I G. 7
`
`42
`
`F I G. 8
`
`MBI_001890
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 4 of 20
`
`5,944,405
`
`10
`~A.~~----~~~----~~~
`
`/
`
`/
`
`/
`
`FIG. 9
`
`1
`
`4
`
`~--~~-------~9
`
`4~~----~~~~~----~10----~
`
`~x< A.
`1
`
`8
`
`9--
`
`1
`
`FIG. 10
`
`FIG. 11
`
`MBI_001891
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 5 of 20
`
`5,944,405
`
`23~
`
`~23
`
`t
`
`I I
`
`~··I
`. •.~;
`
`F I G. 12
`
`8
`
`12
`
`41
`
`12
`
`FIG. 13
`
`MBI_001892
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 6 of 20
`
`5,944,405
`
`FIG. 14 PRIOR ART
`
`4
`100
`
`10
`7
`FIG. 15 PRIOR ART
`
`7
`
`------1:---
`l
`L4
`
`10
`
`FIG. 16 PRIOR ART
`
`MBI_001893
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 7 of 20
`
`5,944,405
`
`SURFACE ROUGHNESS
`
`R MAX
`
`F I G. 17
`
`FIG. 18
`
`M
`
`FIG.I9 ~
`
`M
`
`50
`
`F I G. 20 ??~
`
`M
`
`MBI_001894
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 8 of 20
`
`5,944,405
`
`CUMULATIVE
`HEIGHT OF
`FREQUENCY
`IRREGULARITIES
`DISTRIBUTION (%)
`( ABSOLUTE VALUE )
`28.8
`0
`57. 7 (,um)
`100~~--~~--~~--~~--~~~~
`
`MINIMUM
`VALUE
`
`50
`MEDIAN
`VALUE
`
`100 ( 0/o)
`HEIGHT OF
`IRREGULARITIES
`( ABSOLUTE VALUE )
`
`F I G. 2 I
`
`MBI_001895
`
`

`
`U.S. Patent
`
` P a t e n t
`
`V . s .
`
`
`
` 1 9 9 9
`Aug. 31, 1999
` 3 1 ,
`A u g .
`
` 2 0
`Sheet 9 of 20
` 9 o f '
`S h e e t
`
`5,944,405
`
`s , 9 4 4 , 4 o s
`
`0
`0
`. { )
`I
`
`OOmuN
`
`N
`
`-'
`
`\
`
`! "
`
`~
`
`0
`0
`
`) - .
`
`
`
`C \ J
`C \ J
`.
`( ! )
`
`mm.o_.._
`-L L
`-
`
`.OO_H>.OO_HXzo_EoE_zo<_>_
`
`~
`
`0
`
`0 -
`
`X
`<
`0 -1 - -
`( J -L L .. -<
`
`C D
`~
`
`X
`
`: J
`
`> -
`
`N :
`
`MBI 001896
`
`MBI_001896
`
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 10 of 20
`
`5,944,405
`
`CUMULATIVE
`HEIGHT OF
`FREQUENCY
`IRREGULARITIES
`DISTRIBUTION (%)
`( ABSOLUTE VALUE)
`0
`3_44
`6.88 ( 1-'-m)
`100~~--~~--~~~~--~~-,~~
`
`MINIMUM
`VALUE
`
`50
`MEDIAN
`VALUE
`
`100 ( 0/o)
`HEIGHT OF
`IRREGULARITIES
`( ABSOLUTE VALUE )
`
`F I G. 23
`
`MBI_001897
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 11 of 20
`
`5,944,405
`
`-
`
`~
`
`0
`0
`1.[)
`
`N
`.
`0
`0
`
`~
`C\.1
`
`•
`(.!)
`
`-
`LL.
`
`>-
`.
`
`0
`0
`
`
`
`- X
`
`z
`0
`I-
`<(
`0
`lL
`z
`<..!)
`<(
`~
`
`>-
`
`X
`
`N~
`
`MBI_001898
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 12 of 20
`
`5,944,405
`
`HEIGHT OF
`CUMULATIVE
`IRREGULARITIES
`FREQUENCY
`DISTRIBUTION (%)
`( ABSOLUTE VALUE )
`21.3 ( fLm)
`10.6
`0
`100~~--~~--~~--~~--~-r-,
`
`oL_--~~IITilli~UU~~nn==~~
`I 00 ( 0/o)
`50
`HEIGHT OF
`MEDIAN
`IRREGULARITIES
`VALUE
`( ABSOLUTE VALUE )
`
`MINIMUM
`VALUE
`
`F I G. 25
`
`MBI_001899
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 13 of 20
`
`5,944,405
`
`'\j"
`
`0
`0
`l!)
`
`N
`.
`0
`0
`
`>-
`.
`0
`0
`
`X
`
`z
`0
`1-
`<( u
`LL -z
`
`<.9
`<(
`~
`
`<D
`C\J
`
`(!)
`
`-
`LL
`
`>-
`
`X
`
`N~
`
`MBI_001900
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 14 of 20
`
`5,944,405
`
`CUMULATIVE
`FREQUENCY
`DISTRIBUTION (%)
`
`HEIGHT OF
`IRREGULARITIES
`( ABSOLUTE VALUE )
`10. 1
`20. 3 (,urn)
`0
`100~~--~~--~~--~~--~~~~
`
`o~rrnfrfrrrtltltintitlnllilllDnhhnnD~
`I 00 ( 0/o)
`50
`MEDIAN
`HEIGHT OF
`VALUE
`IRREGULARITIES
`{ ABSOLUTE VALUE )
`
`MINIMUM
`VALUE
`
`F I G. 27
`
`40J.Lm
`
`41
`
`12
`
`F I G. 28
`
`MBI_001901
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 15 of 20
`
`5,944,405
`
`CUMULATIVE
`HEIGHT OF
`FREQUENCY
`IRREGULARITIES
`DISTRIBUTION (%)
`(ABSOLUTE VALUE )
`0
`4.10 ( J.Lffi)
`2_02
`loa~~--~~--~--~~--~~--~~
`
`Q L---~==tlLrrLUD~~~~~~~----~
`50
`100 ( 0/o )
`MEDIAN
`HEIGHT OF
`VALUE
`IRREGULARITIES
`(ABSOLUTE VALUE)
`
`MINIMUM
`VALUE
`
`F I G. 29
`
`MBI_001902
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 16 of 20
`
`5,944,405
`
`o::;t
`
`0
`0
`0
`
`N
`.
`0
`0
`
`>-
`
`0
`0
`
`X
`
`z
`0
`1-
`<l: u
`u..
`z
`(.!)
`<l:
`~
`
`0
`rt')
`
`(!)
`
`-
`LL
`
`>-
`
`X
`
`N~
`
`MBI_001903
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 17 of 20
`
`5,944,405
`
`CUMULATIVE
`FREQUENCY
`DISTRIBUTION (%)
`
`HEIGHT OF
`IRREGULARITIES
`( ABSOLUTE VALUE )
`
`3.06
`0
`too~~--~~--~--~-----.--.--.--~
`
`MINIMUM
`VALUE
`
`50
`MEDIAN
`VALUE
`
`I 00 ( 0/o )
`HEIGHT OF
`IRREGULARITIES
`( ABSOLUTE VALUE )
`
`F I G. 3 I
`
`MBI_001904
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 18 of 20
`
`5,944,405
`
`c;;;t
`
`0
`0
`1.{')
`C\J
`
`N
`
`~
`
`0
`1.{')
`C\J
`
`>-
`
`~
`
`0
`l.()
`
`X
`
`C\J
`rt)
`
`•
`z
`(!)
`0
`~ lJ..
`u
`I.!..
`z
`<.9
`<(
`2
`
`>-
`
`X
`
`N~
`
`MBI_001905
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 19 of 20
`
`5,944,405
`
`0
`0
`cno
`0
`
`0
`l()
`
`t~-
`zQ)
`c:r-
`Oz
`-
`1---t
`~
`
`~3
`
`rt)
`rt)
`
`(.!)
`
`LL
`
`0
`l()
`
`0
`0 b-
`
`(j)
`I
`
`0
`0
`1'-
`II
`:r:
`Q)
`
`N
`.--..
`::r:
`coiN
`-----
`
`I
`
`IT
`\hl
`-~~
`-w
`(.)
`~ q,/
`Zo::
`0:::>
`r-CJ)
`oo
`w
`~r- - -_ J 0
`<.9
`z
`-_ J
`O<J:
`z~ <t\
`-0:: <ro
`~z -
`
`-~
`
`Q)
`
`>-
`r-r-
`-z >w
`CJ)~ CJ)w
`~0::
`(j)::>
`z(j)
`c:r<t
`o::W
`r-~
`
`0
`ill
`I
`
`MBI_001906
`
`

`
`U.S. Patent
`
`Aug. 31, 1999
`
`Sheet 20 of 20
`
`5,944,405
`
`0
`
`~
`II
`:::c
`Q)
`
`N
`
`0
`0
`cno
`----ro
`
`0
`l.()
`
`w
`0
`L1 Zo::
`0:::)
`I- (f)
`oo
`wl(cid:173)
`o:: -_ J
`0<!
`z~
`-0::
`<!o
`:?:z
`
`>-
`1-1--z >w
`
`(/)~
`(f)w
`~0::
`(f)::J
`z(f)
`<!<!
`o::W
`1-::?:
`
`LL
`
`MBI_001907
`
`

`
`5,944,405
`
`1
`FLAT LIGHT SOURCE USING LIGHT(cid:173)
`DIFFUSING SHEET WITH PROJECTIONS
`THEREON
`
`TECHNICAL FIELD
`
`The present invention relates to a fiat light source that can
`be used in applications such as back-lighting for a light
`transmissive type of display device such as a liquid crystal
`display device, an illuminated advertisement, or a traffic
`sign. In particular, it relates to a fiat light source that uses a
`light-diffusing sheet.
`
`BACKGROUND OF THE INVENTION
`
`10
`
`2
`imposed on the light-emitting surface of the optically con(cid:173)
`ductive plate as the lens sheet, the ratio of optical energy
`emitted within angles between 30 and 60 degrees from the
`normal to the light-emitting surface is comparatively high,
`5 but even if the portion within 2 to 4 em of the side edge
`portion of the optically conductive plate is very bright, the
`luminance drops gradually further away from this portion so
`that the edge at the opposite side from the light source is
`noticeably darker.
`If a frosted transparent scattering diffusion plate is used,
`a further problem arises in that the particles oflight-diffusing
`agent within the optically conductive plate absorb some of
`the light, so that the optical energy thereof is lost.
`In addition, interference patterns such as Newton's rings
`15 could be generated by the optical seal between the lens sheet
`and the surface of the optically conductive plate.
`Techniques that have been tried to solve these problems
`include:
`1. An attempt to correct and make uniform the luminance
`distribution within the surface of the optically conductive
`plate by creating a pattern in a light-scattering reflective
`layer on the rear surface of the optically conductive plate,
`such as a dot pattern, in such a manner that the surface area
`of the pattern is decreased closer to the light source and
`.
`~
`increased further away therefrom, as disclosed m Japanese
`Patent Laid-Open No. 1-245,220 and Japanese Utility Model
`Laid-Open No. 6-15,008.
`2. An attempt to correct and make uniform the luminance
`30 distribution within the surface of the optically conductive
`plate by disposing two or more light sources at the side edge
`portions of the optically conductive plate, as disclosed in
`Japanese Patent Laid-Open No. 3-9306.
`3. An attempt to obtain a directed output light that has a
`35 substantially uniform luminance from the entire surface of
`the optically conductive plate, by providing a linear pris(cid:173)
`matic array (an array of prismatic lenses) that partially
`reflects and partially passes light on either the front or rear
`surface of the optically conductive plate, and varying the
`40 angle of inclination of the surfaces of these prisms and
`locally varying the thickness of the optically conductive
`plate, as disclosed in Japanese Patent Laid-Open No.
`62-3226.
`All of the above measures, and others, have problems in
`that it is difficult to provide a completely uniform luminance
`thereby. In addition, technique 1 has a further problem in
`that the dot pattern of the light-scattering reflective layer is
`visible from the side from which light is emitted. Technique
`2 has a further problem in that the space required for the
`entire light source and the power consumption thereof are
`more than doubled.
`Technique 3 has problems in that the form of the optically
`conductive plate is complicated, the fabrication of this
`design is extremely difficult, and it is also difficult to make
`the dot pattern of the light-scattering reflective layer invis(cid:173)
`ible.
`An objective of the present invention is therefore to solve
`the above problems with the prior art and provide a fiat light
`source that implements a uniform and very bright light that
`is limited to a predetermined angular range, and that has no
`variations in luminance due to position within the light
`surface, without increasing the power consumption, amount
`of heat generated, or the size of the entire apparatus.
`DISCLOSURE OF THE INVENTION
`The present invention achieves the above objective by
`providing a fiat light source that uses a light-diffusing sheet
`
`20
`
`Flat light sources that are used for back-lighting in
`devices such as liquid crystal displays (LCDs) are known in
`the art, as described below.
`A first known type of fiat light source is an edge-lit system
`that uses a fiat optically transmissive plate as an optically
`conductive member. The fiat light source used in this system
`causes light to be incident on one or both side edge surfaces
`of the optically conductive member which is formed of a
`transparent fiat plate. Total reflection within the fiat optically
`transmissive plate is utilized to propagate the light through(cid:173)
`out the entire optically conductive plate. Part of the thus
`propagated light becomes diffused reflected light of less than
`the critical angle from a light-scattering reflective plate on
`the rear surface of the optically conductive plate, and thus
`diffused light is emitted from the outer surface of the
`optically conductive plate (refer to Japanese Utility Model
`Laid Open No. 55-162,201).
`A second known type of fiat light source has a lens sheet
`wherein one surface has projections and the other surface is
`smooth, which is placed with the projection side thereof on
`the outer surface of the optically conductive plate of the fiat
`light source of the above first type. The light-focusing action
`of this lens is utilized to ensure that the diffused, reflected
`light is diffused uniformly and isotropically within a prede(cid:173)
`termined angular range (refer to Japanese Utility Model Laid
`Open No. 4-107,201).
`The above described lens sheet could be used in combi(cid:173)
`nation with a frosted transparent diffusion plate (a frosted
`transparent sheet) formed by dispersing particles of a light(cid:173)
`diffusing agent such as Ti0 2 within a transparent plastic. In 45
`such a case, the optical energy of the light source is
`distributed in a more concentrated manner within a prede(cid:173)
`termined limited angular range, than when a frosted trans(cid:173)
`parent diffusion plate alone is placed over the optically
`conductive plate (refer to U.S. Pat. No. 4,729,067 and 50
`Japanese Patent Laid Open No. 61-55,684). Moreover, a
`uniform and highly isotropic diffused light can be obtained
`within this angular range.
`However, both of the above prior-art techniques have
`problems. The first one simply places a light-scattering 55
`reflective plate on the rear surface of the optically conduc(cid:173)
`tive plate so that the emitted light has a comparatively sharp
`distribution that peaks at an angle of 60 degrees to the
`normal of the surface of the optically conductive plate.
`Therefore a phenomenon is observed in which the degree of 60
`luminance is insufficient in the normal direction (the forward
`direction) where brightness is most required, while optical
`energy is wasted in the lateral directions where it is com(cid:173)
`pletely unnecessary.
`The second prior-art technique has a problem in that, 65
`when a lenticular sheet that comprises an array of a large
`number of individual triangular prismatic lenses is super-
`
`MBI_001908
`
`

`
`5,944,405
`
`5
`
`3
`formed of a transparent material containing no particles of a
`light-diffusing agent. The front surface of this light-diffusing
`sheet has minute irregularities formed at random; these
`minute irregularities have a surface roughness of at least the
`wavelength of the light from the light source, but no more
`than 100 ,urn; and, when a cumulative frequency distribution
`curve of the heights of the minute irregularities is plotted,
`with the percentage of the cumulative frequency distribution
`of the heights of these irregularities along the Y-axis and the
`heights of the minute irregularities along the X-axis, the
`cumulative frequency distribution curve has a convex por(cid:173)
`tion oriented towards a lower side of coordinates and the
`average value of the heights of the minute irregularities is
`greater than a median value thereof.
`A light source is disposed along at least one side edge
`surface of this light-diffusing sheet, and the light-diffusing
`sheet can be provided superimposed on a light-emitting
`surface of an optically conductive member that is a fiat
`optically transmissive plate, or an optically conductive
`member that has a rectangular cavity therein, where the 20
`optically conductive member has a light-reflecting layer on
`the rear surface thereof.
`The light-diffusing sheet may also be provided in such a
`manner as to cover a window in a lamp housing. This lamp
`housing is configured to contain a light source, light- 25
`reflecting wall surfaces of the lamp housing cover the rear
`and side surfaces of the light source, and the window is
`formed in the front surface of the light source.
`When the above described optically conductive member
`is formed of a fiat, optically transmissive plate, the front 30
`surface of the optically conductive member may be a fiat
`surface having a surface roughness less than the wavelength
`of the light of the light source.
`A sheet that is a one-dimensional or two-dimensional
`array of convex or concave lenses may be superimposed
`over the light-diffusing sheet. Similarly, another, identical
`light-diffusing sheet may be superimposed over the first
`light-diffusing sheet.
`
`4
`FIG. 11 is a sectional view showing how some of the light
`rays proceeding towards the exterior of the optically con(cid:173)
`ductive plate are totally reflected while others are
`transmitted, when the light-diffusing sheet of the present
`invention is used;
`FIG. 12 shows an example of the method of fabricating
`the light-diffusing sheet of the present invention;
`FIG. 13 is a perspective view of an example of the
`light-diffusing sheet of the present invention, fabricated by
`10 the fabrication method shown in FIG. 12;
`FIG. 14 is a cross-sectional view through an edge-lit fiat
`light source of the prior art, showing the lack of a lens sheet;
`FIG. 15 is a perspective view of the edge-lit fiat light
`15 source of the prior art, showing a lens sheet having a fiat rear
`surface;
`FIG. 16 is a sectional view of the configuration of FIG.
`15;
`FIG. 17 is a graph of cumulative frequency distribution
`f(R), with surface roughness (that is, the percentage of
`cumulative frequency distribution of depths R of concavities
`in the mold) plotted along the X-axis and with surface
`roughness (that is, the depths R of the concavities in the
`mold) plotted along the Y-axis, in a fabrication mold for
`imprinting projections of the light-diffusing sheet in accor(cid:173)
`dance with the present invention;
`FIG. 18 is a sectional view of a fabrication mold having
`the characteristic of the cumulative frequency distribution
`curve fA(R) in FIG. 17;
`FIG. 19 is a is a sectional view of a fabrication mold
`having the characteristic of the cumulative frequency dis(cid:173)
`tribution curve fB(R) in FIG. 17;
`FIG. 20 is a sectional view illustrating undercutting
`formed by aggregations of minute spherical particles of the
`35 metal chrome, during the matte-plating of chrome onto the
`indented surface of the roll mold used for fabrication;
`FIG. 21 shows a graph relating to the heights of projec(cid:173)
`tions of the light-diffusing sheet used in this invention (that
`is, the surface roughness of the light-diffusing sheet) and the
`distribution thereof as a cumulative frequency distribution
`curve f(R), with surface roughness (that is, the percentage of
`cumulative frequency distribution of heights R of the peaks)
`plotted along the X-axis and surface roughness (that is, the
`heights R of the peaks) along theY-axis, in a case in which
`the cumulative frequency distribution curve has a downward
`convexity and a relationship (average value~median value)
`is satisfied;
`FIG. 22 is a fragmentary expanded three-dimensional
`50 visualization of measurements showing the projections of a
`light-diffusing sheet used in this invention having the cumu(cid:173)
`lative frequency distribution characteristics of FIG. 21;
`FIG. 23 shows a graph relating to the heights of projec(cid:173)
`tions of the light-diffusing sheet used in this invention (that
`55 is, the surface roughness of the light-diffusing sheet) and the
`distribution thereof as a cumulative frequency distribution
`curve f(R), with surface roughness (that is, the percentage of
`cumulative frequency distribution of heights R of the peaks)
`plotted along the X-axis and surface roughness (that is, the
`60 heights R of the peaks) plotted along theY-axis, in a case in
`which the cumulative frequency distribution curve has a
`downward convexity and a relationship (average
`value~median value) is satisfied;
`FIG. 24 is a partial expanded three-dimensional visual-
`65 ization of measurements showing the projections of a light(cid:173)
`diffusing sheet used in this invention having the cumulative
`frequency distribution characteristics of FIG. 23;
`
`45
`
`40
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a perspective view of an example of a trans(cid:173)
`missive type of display device using an edge-lit type of fiat
`light source in accordance with this invention;
`FIG. 2 is a perspective view of an example of a trans(cid:173)
`missive type of display device using a back-lit type of fiat
`light source in accordance with this invention;
`FIG. 3 is a cross-sectional illustrative view through an
`example of an edge-lit fiat light source, showing groups of
`projections formed on both surfaces of the light-diffusing
`sheet;
`FIG. 4 is a perspective view of an example of a lens sheet
`used by the present invention;
`FIG. 5 is a perspective view of another example of a lens
`sheet used by the present invention;
`FIG. 6 is a perspective view of a further example of a lens
`sheet used by the present invention;
`FIG. 7 is a perspective view of yet another example of a
`lens sheet used by the present invention;
`FIG. 8 is a perspective view of an example of two
`superimposed lens sheets used by the present invention;
`FIG. 9 is a sectional view showing the paths of light rays
`travelling from the interior of the optically conductive plate
`to the outside thereof;
`FIG. 10 is a sectional view showing light rays that have
`been emitted by the tunnel effect from the optically conduc(cid:173)
`tive plate as they proceed into the lens sheet;
`
`MBI_001909
`
`

`
`5,944,405
`
`5
`FIG. 25 is a graph showing the heights of projections of
`the light-diffusing sheet used in this invention (that is, the
`surface roughness of the light-diffusing sheet) and the dis(cid:173)
`tribution thereof as a cumulative frequency distribution
`curve f(R), with surface roughness (that is, the percentage of 5
`cumulative frequency distribution of heights R of the peaks)
`plotted along the X-axis and surface roughness (that is, the
`heights R of the peaks) plotted along theY-axis, in a case in
`which the average value of R has a maximum at 52% and the
`cumulative frequency distribution curve has a downwardly
`convex portion and an upwardly convex portion;
`FIG. 26 is a partial expanded three-dimensional visual(cid:173)
`ization of measurements showing the projections of a light(cid:173)
`diffusing sheet used in this invention having the cumulative
`frequency distribution characteristics of FIG. 25;
`FIG. 27 is a graph showing the heights of projections of 15
`the light-diffusing sheet used in this invention (that is, the
`surface roughness of the light-diffusing sheet) and the dis(cid:173)
`tribution thereof as a cumulative frequency distribution
`curve f(R), with surface roughness (that is, the percentage of
`cumulative frequency distribution of heights R of the peaks) 20
`plotted along the X-axis and surface roughness (that is, the
`heights R of the peaks) plotted along theY-axis, in a case in
`which the cumulative frequency distribution curve is linear;
`FIG. 28 is a partial enlarged perspective view of projec(cid:173)
`tions of a light-diffusing sheet formed of ridges of a rect- 25
`angular equilateral triangular sectional shape and having the
`cumulative frequency distribution curve of FIG. 27;
`FIG. 29 is a graph showing the heights of projections of
`the light-diffusing sheet used in this invention (that is, the
`surface roughness of the light-diffusing sheet) and the dis- 30
`tribution thereof as a cumulative frequency distribution
`curve f(R), with surface roughness (that is, the percentage of
`cumulative frequency distribution of heights R of the peaks)
`plotted along the X-axis and surface roughness (that is, the
`heights R of the peaks) plotted along theY-axis, in a case in 35
`which the cumulative frequency distribution curve has a
`partial upwardly convex portion and a partial downwardly
`convex portion, and the average value is less than the
`median value.
`FIG. 30 is a partial expanded three-dimensional visual-
`ization of measurements showing the projections of a light(cid:173)
`diffusing sheet used in this invention having the cumulative
`frequency distribution characteristics of FIG. 29;
`FIG. 31 is a graph showing the heights of projections of
`the light-diffusing sheet used in this invention (that is, the
`surface roughness of the light-diffusing sheet) and the dis- 45
`tribution thereof as a cumulative frequency distribution
`curve f(R), with surface roughness (that is, the percentage of
`cumulative frequency distribution of heights R of the peaks)
`plotted along the X-axis and surface roughness (that is, the
`heights R of the peaks) plotted along theY-axis, in a case in 50
`which the cumulative frequency distribution curve has a
`downward convexity over the entire region thereof;
`FIG. 32 is a partial expanded three-dimensional visual(cid:173)
`ization of measurements showing the projections of a light(cid:173)
`diffusing sheet used in this invention having the cumulative 55
`frequency distribution characteristics of FIG. 32;
`FIG. 33 shows the angular distribution of luminance of a
`light-emitting surface of a fiat light source (Example 1 and
`Comparative Example 1); and
`FIG. 34 shows the angular distribution of luminance of a 60
`light-emitting surface of another fiat light source (Example
`8) of this invention.
`
`40
`
`BEST MODES FOR CARRYING OUT 1HE
`INVENTION
`Embodiments of a fiat light source in accordance with the
`present invention and a display device using this fiat light
`
`10
`
`6
`source will be described below with reference to the accom(cid:173)
`panying drawings.
`An edge-lit type of fiat light source is shown in FIG. 1. In
`this figure, reference numeral 1 denotes an optically con(cid:173)
`ductive plate, where this optically conductive plate 1 is
`configured of a solid optically transmissive fiat plate. A light
`source such as a linear light source 3 is provided along one
`edge surface of this optically conductive plate 1. A reflective
`mirror 5 is provided behind the light source 3. Light emitted
`from the light source 3 enters the interior of the optically
`conductive plate 1 either directly or after being reflected by
`the reflective mirror (also a lamp housing with reflective
`surfaces) 5. It is reflected internally as shown for example in
`FIG. 3 or it is emitted directly outside from within the
`optically conductive plate 1. A light reflecting layer 2 is
`provided on the rear surface of the optically conductive plate
`1. The surface of the optically conductive plate 1 opposite to
`the light reflecting layer 2 forms a light-emitting surface. A
`light-diffusing sheet 8 is provided facing this light-emitting
`surface, and light emitted through the light-emitting surface
`passes through the light-diffusing sheet 8. Light that has
`passed through the light-diffusing sheet 8 passes through a
`lens sheet 4 and then reaches a transmission type display
`device 6. A gap 9 is formed between the light-diffusing sheet
`8 and the optically conductive plate 1, and between the
`light-diffusing sheet 8 and the lens sheet 4. Projections 41
`that will be described in more detail later are formed on the
`surfaces of the light-diffusing sheet 8 facing these gaps 9.
`Instead of being solid, the optically conductive plate 1
`could have an empty structure. In such a case, the light(cid:173)
`emitting surface of the solid optically conductive plate 1 and
`the surface thereof in contact with the light reflecting layer
`2 would each be in the form of a fiat plate, with the space
`therebetween forming a rectangular cavity.
`With a back-lit light source as shown in FIG. 2, the light
`source 3 is a linear or point light source and accommodated
`within a lamp housing 5. The lamp housing 5 extends over
`the rear and sides of the light source 3 and acts as reflective
`surfaces for reflecting the light from the light source 3 in the
`direction of the light-diffusing sheet 8.
`In FIGS. 1 and 2, reference number 100 denotes a fiat
`light source in its entirety and reference number 200 denotes
`a display device in its entirety.
`In accordance with this present invention, projections 41
`are obtained by forming minute irregularities at random
`(such as in a sharkskin pattern or a pear skin pattern) over
`the entire surface of the light-diffusing sheet 8. These minute
`irregularities have a surface roughness that is at least the
`wavelength of the light emitted from the light source but is
`no more than 100 ,urn. When the percentages of the cumu-
`lative frequency distribution of the heights of the minute
`irregularities are plotted along the Y-axis and the heights of
`these minute irregularities along the X-axis, the cumulative
`frequency distribution curve should typically have a convex
`portion oriented towards the lower side of the coordinates
`and the average value of the height of the minute irregu(cid:173)
`larities should be greater than the median thereof.
`The light-diffusing sheet 8 used by the present invention
`is formed from a transparent material. In this case, the
`transparent material may be a (meth)acrylic ester such as
`polymethyl (meth)acrylate or polyethyl (meth)acrylate
`[where "(meth)acrylate" means either methacrylate or acry(cid:173)
`late throughout the specification] or a copolymer thereof; a
`65 polyester such as polyethylene terephthalate or polybutylene
`terephthalate; a thermoplastic resin such as a polycarbonate,
`polystyrene or polymethylpentene resin; an ultraviolet light-
`
`MBI_001910
`
`

`
`5,944,405
`
`5
`
`10
`
`20
`
`7
`or electron beam-curable, transparent resin which has been
`crosslinked and cured by ultraviolet rays or electron beams;
`a transparent glass; or a transparent ceramic material.
`As ultraviolet light curable resins or electron beam cur(cid:173)
`able resins, compositions comprising a prepolymer, oligo(cid:173)
`mer and/or monomer having, in its molecule, a polymeriz(cid:173)
`able unsaturated bond such as a (meth)acryloyl group or a
`(meth)acryloyloxy group or an epoxy group. In this
`connection, the term "(meth)acryloyl" is used to mean
`"acryloyl" or "methacryloyl" throughout the specification.
`Such prepolymer and oligomer include an acrylate such as
`urethane (meth)acrylate, polyester (meth)acrylate epoxy
`(meth)acrylate, and an unsaturated polyester. Further, a
`dipentaerythritol penta (meth)acrylate can be exemplified as
`the monomer used in this case.
`I